Association of Obesity With Maternal and Cord Blood Penicillin Levels in Women With Group B Streptococcus Colonization

OBJECTIVE:To compare maternal and cord blood penicillin concentrations in women with and without obesity who are receiving intrapartum group B streptococcus (GBS) prophylaxis. METHODS:We performed a prospective cohort study of term women receiving intrapartum penicillin prophylaxis for GBS colonization (determined by antenatal rectovaginal culture). The following outcomes were compared between obese (body mass index [BMI] 35 or higher at delivery) and nonobese (BMI less than 30 at delivery) groupspenicillin concentration in maternal blood (after two penicillin doses) and umbilical cord blood, GBS rectovaginal colonization status on admission and after two completed doses, and neonatal GBS colonization (using a postnatal ear swab). Fifty-five women were needed to detect a 0.75 SD difference in cord blood penicillin concentrations. RESULTS:Fifty-five women were enrolled and had all specimens collected; 49 had complete data for analysis (obese n=25, nonobese n=24). There was no difference in the median maternal penicillin concentration between groups (obese 4.2 micrograms/mL vs nonobese 4.0 micrograms/mL, P=.58). There was, however, a 60% lower median cord blood penicillin concentration in the obese compared with the nonobese group (2.7 micrograms/mL vs 6.7 micrograms/mL, respectively, P